Some of the refrigerating air conditioners for use in air conditioners or refrigerating machines comprise, in order to improve the COP (Coefficient of Performance), a main compressor for compressing a refrigerant and an expander including an expansion mechanism for expanding the refrigerant and a sub-compression mechanism for converting the expansion energy in the expansion mechanism into a mechanical energy. In such the refrigerating air conditioner, in order to prevent the decrease in the reliability of the main compressor and the expander due to the sticking or abnormal wear of the machine parts, the oil levels in the main compressor and the expander must be regulated so that shortage of the lubricating oil does not occur.
Therefore, in the conventional refrigerating air conditioner, the pressure within the hermetic vessel of the main compressor is arranged to be maintained at the suction pressure, the suction pipe to the main compression mechanism is disposed within the hermetic vessel, its opening portion is positioned above the oil level of the lubricating oil maintained in the hermetic vessel, and an oil recovery hole is provided below the opening portion and at the upper limit position of the adequate oil level within the hermetic vessel of the main compressor (see Patent Document 1, for example).
Also proposed is a refrigerating air conditioner having a first compressor and a second compressor and an equalizing oil pipe communicating the bottom portion of the first compressor with the bottom portion of the second compressor is provided (see Patent Document 2 and Patent Document 3, for example).
Patent Document 1: Japanese Patent Laid-Open No. 2004-325019 (page 8, FIGS. 8 and 9).
Patent Document 2: Japanese Patent Laid-Open No. 7-103594 (pages 3-4, FIG. 1).
Patent Document 3: Japanese Patent Laid-Open No. 6-109337, (page 3, FIG. 1)